As an organic device, an EL element is widely known. The EL element has an organic compound as a light emitting layer, and current is applied to the light emitting layer by applying voltage by a pair of electrodes provided so as to sandwich the light emitting layer, and photons in accordance with the current density are released; thus, the EL element serves as a light source. In applying voltage to the light emitting layer in an EL element, an alloy of Mg (magnesium) and Ag (silver) or an alloy of Li (lithium) and Al (aluminum), each of the elements has low work function, has been used for a metal electrode of a cathode side in order to lower the electron injection barrier against an organic compound which is regarded as an insulator, and to improve the adhesion with a surface of the light emitting layer.
As to the alloy electrode of Mg or Li, element deterioration due to oxidation of the electrode or the like is caused, and moreover, there are various limitations. Correspondingly, reviewing a metal electrode itself, proposed is an organic element in which a metal doping layer is formed by doping a metal having a work function of 4.2 [eV] or less on a surface of the light emitting layer in contact with a cathode electrode; thus, a layer having an electron supplying properties is provided on the cathode side as a hole injection layer is provided on the cathode side of the light emitting layer (see Patent document 1).    Patent document 1 Japanese Patent Laid-Open No. 10-270171
In a technique disclosed in the above Patent document 1, the electron injection barrier for the light emitting layer from the cathode side can be lowered by providing the metal doping layer; however, a selection of the materials is limited so that the adhesion between the metal doping layer and the metal electrode is secured; further, the kind of metal is also limited.
In addition, a multiphoton emission (MPE) element having a structure in which a plurality of light emitting layers are connected in sequence is also proposed lately. In order to realize this MPE element, an internal electrode provided between light emitting layers adjacent to each other need to have a function of injecting electrons into one of the light emitting layers and injecting holes into the other light emitting layer. Therefore, the technique disclosed in the above Patent document 1 cannot be applied to the internal electrode for an MPE element.